I have a user with a new high-end MacBook Pro that can't use the internet. He can connect to either our wired or wireless network and do things like browse file shares, but can get no further.
When I brought the machine in for testing, I found that I could do an nslookup just fine, and I'm able to ping addresses returned by nslookup just fine. I'm even able to bring up web pages by entering the IP address into the address bar directly. However, when I try to ping the domain name rather than the IP address, it just sits there. So apparently I can either do name resolution or communicate with an address, but not both at the same time.
Again, these symptoms occur on both the wired and wireless network. Other machines on our network, including a few other Macs, don't have this issue.